1. Field of the Invention
This invention relates to a method and a device for controlling the fuel injection quantity of an electronic control diesel engine, and more particularly to improvements in a method and a device for controlling fuel injection quantity, being suitable for use in a diesel engine provided with an electromagnetic spill type fuel injection pump, wherein a fuel injection quantity is controlled by an electromagnetic spill valve on-off operated at a target spill angle in accordance with an angle count number and a time count number of an engine rotation angle signal, based on the engine rotation angle signal outputted through a predetermined crank angle.
2. Description of the Prior Art
Along with the development in the electronic control techniques, particularly, the digital control techniques in recent years, there has been commercialized the so-called electronic control diesel engine, wherein a fuel injection pump of the diesel engine is electronically controlled.
There are various methods of electronically controlling the fuel injection pump. One of the fuel injection pumps is a so-called electromagnetic spill fuel injection pump as disclosed in U.S. Pat. No. 4,520,780 for example, wherein fuel spill in the fuel injection pump is controlled by an electromagnetic spill valve. In this electromagnetic spill type fuel injection pump, at a spill timing where the fuel injection quantity reaches a target value, a spill port is opened by an electromagnetic spill valve to control the termination of fuel injection, so that the fuel injection quantity is controlled.
Normally, the electromagnetic spill valve is on-off operated by a control unit for taking in a detection signal from an engine rotation sensor (NE sensor) for detecting an engine rotation angle and an engine speed, including a rotation angle gear wheel fixed to a driving shaft of the fuel injection pump, and an electromagnetic pickup provided on a roller ring, for detecting a gear of the rotation angle gear wheel, and for a calculating and determining a fuel injection quantity as referenced from a rotation angle signal. More specifically, the roller ring moves in accordance with the position of a timer piston, whereby a pressure feed timing of a plunger is varied to change the injection timing. Since the roller ring and a plunger lift are associated in positional relationship with each other at a rate of 1:1, an engine rotation pulse (NE pulse) and a plunger lift are associated with each other at the rate of 1:1 as shown in FIG. 7.
The electromagnetic spill valve is of a normally open type, energized as referenced from the NE pulse position, turned on (fuel injection) at No. 9 pulse before the pressure feed of the plunger, and turned off (injection cut by the spill) at a spill angle ANGspv, where a target fuel injection quantity is obtained.
More specifically, upon a lapse of a time duration (time count number) TSPon corresponding to a time count angle .theta.rem (.degree.CA) as referenced from an end point of an angle count number Cangl of the engine rotation angle signal, the electromagnetic spill valve is turned off. The time conversion of the time count angle .theta.rem to the time duration TSPon is determined from a preceding engine rotation time duration T180.sub.i-1 through 180.degree. CA for example.
However, the time count angle .theta.rem may have a large dispersion due to factors such as the dispersion of fuel injection quantities of a fuel injection nozzle and the fuel injection pump, the change with time (the spill angle ANGspv varies so as to be a target rotation due to idle speed control), the press-in dispersion of the rotation angle gear wheel, the variations in the fuel injection quantity due to an automatic transmission, an air conditioner, a power steering unit, electric loads, etc., the change in the fuel injection quantity due to the fuel temperature and nature, and the like, whereby the angle count number Cangl as being the reference may vary. To prevent the delay due to the multiple interrupts such as the interrupt of the NE sensor, ignition interrupt, 5 millisecond interrupt, interrupt of analogue-digital conversion when the angle count number Cangl varies as described above, the spill time duration TSPon corresponding to the time count angle .theta.rem is determined from the preceding NE pulse rising position as shown in FIG. 8(A) when it is within the set time duration, e.g. 220 microseconds from the NE pulse rising position. While, it is 220 microseconds or more from the NE pulse rising position, it is conceivable that the spill time duration TSPon is left as it is as shown in FIG. 8(B). However, according to the method of this type, when the NE pulse rising as being the reference is changed over, a dispersion of 220 microseconds (0.9.degree. CA, which corresponds to the fuel injection quantity 3 mm.sup.3 /stroke at the time of idling).
In consequence, due to the dispersion factor of the aforesaid time count angle .theta.rem (TSPon), the timing of turning off the electromagnetic spill valve suffers from a great dispersion of the fuel injection quantity just at the time of change-over of the NE pulse, particularly, in the proximity of the idling including a low rotation area, thus presenting a problem of that the vibrations of the engine become very high.
In FIGS. 7 and 8, the NE pulses are shown equidistantly, however, when the engine rotates practically, intervals in the proximity of No. 0 pulse is wide (the engine speed is low) and the intervals in the proximity of No. 8 pulse are narrow (the engine speed is high). Moreover, as the engine speed momentarily varies even within the intervals of the NE pulses, the association of the time duration with the angle is not at the rate of 1:1. In consequence, the engine rotation time duration through 11.25.degree. CA is not equal to 1/16 (AVT45/4) of the preceding engine rotation time duration through 180.degree. CA, whereby, at the change-over point of the reference position of the NE pulse, there is a considerable difference between the spill valve off timing calculated from No. 5 pulse and one calculated from No. 6 pulse for example. As the result, at the change-over point of the reference position of the NE pulse, the dispersion of the fuel injection quantity control due to the dispersion of the spill valve off timing is increased.
This tendency is the largest in the proximity of idling. At high speed rotation, the fluctuations in rotation due to the compression and explosion of the engine is decreased, whereby it becomes negligible.
Additionally, as the methods of raising the detecting accuracy in detecting the rotation angle, there have been proposed that the tooth number of the rotation angle gear wheel is increased, and a multiplicity of magnetic poles different in polarity are provided on a circumference, which are adjacent to one another, as proposed by one of the applicants in Japanese Patent Application No. 104949/1984. Any way, the dispersion of the fuel injection quantity due to the dispersion of the angle count number cannot be efficiently prevented.